Integrated circuit fabrication, or semiconductor processing, is a highly competitive industry in which cost savings from increases in the speed of processing or reduction in the number of steps in processing is highly amplified over the thousands of wafers processed, each of which represents hundreds of integrated circuit chips or dies.
One example of the complexities of integrated circuit processing is in manufacturing different types of circuits on different regions of an integrated circuit. For example, in manufacturing memory devices, dense repeating patterns of memory cells are fabricated in an array region, while complex but less dense logic circuits are created in a peripheral region adjacent the array. Transistors in the logic region are often arranged as CMOS circuits, including both NMOS and PMOS cross-latched transistors, whereas simpler designs are employed in the array region, and more dense transistor arrangements are usually employed in the array. In one example, planar transistors are formed in the peripheral region, with the gate dielectric and gate electrode formed above the substrate, while recessed access devices (RADs) are formed in the periphery to allow for greater density of circuitry. Typically different materials are employed for the different parts of the transistors in the array versus the periphery. Thus, conventionally, the array is masked off while peripheral devices are constructed, and vice versa.